Current science believes that we only have a specific amount of each element found on earth. Based on this principle at some point we will eventually run out of the things that we find important. While it will likely be quite a while until we run out, we will eventually run out of steel.
It is undeniable that as the developing nations of the world continue to expand and catch up in industrial manufacturing then we will see an exponential growth in the need for steel of all grades. Low-grade steel is a limited resource and urgently needs to be dealt with as such.
As long as we keep wasting resources the way we do, steel could very well run-out, just like fossil fuels, there is only so much in the earth and it will run out, the best thing to do is to start recycling already used steel to keep from mining for more.
Scientists will not run out of low-grade steel anytime soon. Yes, iron and coal are finite resources. Yes, governmental restrictions are making it more difficult to extract coal, especially in an economical way. However, whenever claims are made that we're about to run out of a natural resource, it never happens. Why? New deposits get discovered every time. Furthermore, due to technological advances, the deposits that are currently known end up yielding more and more than they used to.